The law of conservation of momentum states that in an isolated system, the total momentum before a collision is equal to the total momentum after the collision.

Here's a breakdown:

* Isolated System: A system where no external forces are acting on it. Think of a closed container in space with no friction.

* Momentum: A measure of an object's mass in motion. It's calculated as mass (m) multiplied by velocity (v): p = mv

* Total Momentum: The sum of the momentum of all objects in the system.

In simpler terms: When objects collide within an isolated system, the total amount of motion (momentum) stays the same. This means that even though the objects' velocities change, the overall amount of motion before and after the collision remains constant.

Important Note: This law only applies to isolated systems where external forces are negligible. In real-world scenarios, factors like friction and air resistance can affect momentum.